L 26

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Questions and Answers

What primarily contributes to the elastic property of the lungs?

Tissue elastic forces from smooth muscle contraction

Elastic forces generated by the movement of the diaphragm

Elastic forces from elastin and collagen fibres in lung parenchyma (correct)

Elastic properties of the pulmonary arteries

In normal adults, what is the total compliance of both lungs together?

150 ml of air per cm of water transpulmonary pressure

200 ml of air per cm of water transpulmonary pressure (correct)

300 ml of air per cm of water transpulmonary pressure

250 ml of air per cm of water transpulmonary pressure

How are the tissue elastic forces and fluid air surface tension elastic forces divided in total lung elasticity?

1/4 tissue elastic forces and 3/4 fluid air surface tension forces

1/2 tissue elastic forces and 1/2 fluid air surface tension forces

1/3 tissue elastic forces and 2/3 fluid air surface tension forces (correct)

2/3 tissue elastic forces and 1/3 fluid air surface tension forces

What is the compliance of the lungs and chest wall combined in terms of lung volume change per unit change in airway/alveolar pressure?

0.13 L/cm of H2O Signup and view all the answers

What represents the compliance of the lungs alone, excluding the thoracic cage?

0.20 L/cm of H2O Signup and view all the answers

What represents a condition where lung compliance is increased?

Emphysema Signup and view all the answers

Which physiological component directly affects the slope of the pressure-volume curve?

Pressure variations Signup and view all the answers

How does a stiffer lung affect the pressure required for inflation?

It requires more pressure for inflation Signup and view all the answers

In which condition would the compliance curve be shifted downward and to the right?

Pulmonary congestion Signup and view all the answers

What is the normal compliance value expressed in liters per cmH2O?

0.1 L/cmH2O Signup and view all the answers

Which of the following conditions specifically causes decreased lung compliance?

Pulmonary fibrosis Signup and view all the answers

What is the effect of supine position on lung compliance?

Decreases compliance Signup and view all the answers

Which condition is associated with a flatter compliance curve?

Restrictive lung disease Signup and view all the answers

Which part of the pleura is inseparable from the lung tissue itself?

Visceral pleura Signup and view all the answers

What is the term used to describe the measure of expansibility of the lungs?

Compliance Signup and view all the answers

Which type of pleura covers the thoracic surface of the diaphragm?

Diaphragmatic pleura Signup and view all the answers

What is the significance of the costo-diaphragmatic recess in the respiratory system?

It acts as a reserve space for lung expansion during inspiration. Signup and view all the answers

Which pleura is subdivided based on the structures it lines?

Parietal pleura Signup and view all the answers

At which rib level does the lower limit of the pleura approximately sit at the mid-axillary line?

10th rib Signup and view all the answers

Which of these statements about lung compliance is false?

Higher compliance indicates a stiffer lung. Signup and view all the answers

The costo-mediastinal recess is located between which two pleural layers?

Costal and mediastinal pleurae Signup and view all the answers

What is the primary role of surfactant in the alveoli during expiration?

To prevent collapse of the alveoli Signup and view all the answers

How does the concentration of surfactant change when the size of the alveolus decreases?

Concentration increases which helps to lower surface tension Signup and view all the answers

What effect does surfactant have on lung compliance?

It increases lung compliance by reducing surface tension Signup and view all the answers

According to Laplace's Law, what happens to pressure when the radius of an alveolus is halved?

Pressure is doubled Signup and view all the answers

What is a consequence of surfactant deficiency in the lungs?

High surface tension which may lead to pulmonary edema Signup and view all the answers

Which component is NOT typically found in alveolar surfactant?

Carbohydrates Signup and view all the answers

What important function does surfactant perform related to alveolar stability?

Equalizes pressure in alveoli of different radii Signup and view all the answers

What is the role of surfactant in relationship to immune function in the lungs?

It regulates lung inflammation and facilitates phagocytosis Signup and view all the answers

What is the role of tubular myelin in the alveoli?

It organizes surfactant phospholipids into a complex lattice. Signup and view all the answers

Which aspect of surfactant metabolism aids in maintaining the surfactant balance in the alveoli?

Recycling of phospholipids back into type II cells. Signup and view all the answers

What is the primary consequence of insufficient surfactant secretion in premature infants?

Increased lung collapse tendency. Signup and view all the answers

What physiological condition is primarily affected by the surfactant components in newborns?

Respiratory distress syndrome. Signup and view all the answers

How are surfactant components initially produced within the cells?

From precursors in the endoplasmic reticulum. Signup and view all the answers

What is a common treatment for infants with surfactant deficiency?

Administration of antenatal steroids. Signup and view all the answers

During exocytosis, where are surfactant components secreted?

Into the liquid lining of the alveolus. Signup and view all the answers

What is a significant factor affecting the lung development of a fetus related to surfactant production?

Timing of surfactant secretion during gestation. Signup and view all the answers

Study Notes

Respiratory System

This presentation covers the respiratory system, focusing on the pleura, lung compliance, and pulmonary surfactant.

Learning Outcomes

To understand the pleura and diaphragmatic recesses
To define lung (pulmonary) compliance and its determinants
To describe the role of elastic fibers in lung parenchyma compliance
To elucidate the role of pulmonary surfactant concerning surface tension and its clinical ramifications

Pleura

The pleura is a closed serous sac.
It has two layers: visceral and parietal pleurae.
These layers are continuous around the lung roots and pulmonary ligaments.
Visceral pleura closely adheres to the lung, while the parietal pleura lines the thoracic cavity.

Pleura - Layers

Parietal pleura is subdivided into costal, diaphragmatic, cervical and mediastinal pleurae.
Costal pleura lines the inner surface of the sternum, ribs, costal cartilages, and intercostal spaces.
Diaphragmatic pleura covers the thoracic surface of the diaphragm.
Cervical pleura extends from the first rib to the apex of the lung, connecting with the mediastinal pleura.
Mediastinal pleura forms the lateral boundary of the mediastinum and covers the mediastinal surface of the lungs.

Recesses of Pleura

Pleural recesses are widenings in the pleural cavity.
They act as reserve spaces for lung expansion during deep inspiration.
Costomediastinal recess: Between costal and mediastinal pleurae.
Costodiaphragmatic recess: Between costal and diaphragmatic pleurae. These recesses are prominent in reference to the cardiac notch of the lung. At mid-clavicular, mid-axillary, and scapular lines respectively, the lower limit of the pleura is along ribs 8, 10 and 12. The lower border of the lung follows ribs 6, 8 and 10.
These recesses allow for maximum lung expansion during inspiration. If fluid leaks into the pleural cavity, this fluid first collects in the costodiaphragmatic recess.

Determinants of Lung Compliance

Lung compliance is the measure of lung expansibility.
Two factors determine lung compliance
- Elastic Property of the lung.
  - Tissue elastic properties due to elastin and collagen fibers in lung parenchyma and elastic forces from the surface tension of lung alveolar fluid.
- Elastic property of the thoracic cage is due to the rib's elastic nature, muscle, and tendon

Lung Compliance

The total compliance of both lungs in a normal adult is 200 ml of air per cm of water transpulmonary pressure.
Tissue elastic forces account for 1/3 of the total lung elasticity, while fluid surface tension elastic forces contribute 2/3.
The total amount of work done during breathing is the loop area.

Pressure-Volume Curve

Lung compliance is a static measurement of lung and chest recoil (or ability to return).
The curve during inflation differs from the curve during deflation, which is termed hysteresis.
Lung volume at any given pressure during inhalation is less than the lung volume at the same pressure during exhalation.

Compliance Calculations

Normal Compliance: 0.1 liter/cmH2O
Low compliance: 0.05 liter/cmH2O
High compliance: 0.17 liter/cmH2O

Factors Affecting Lung Compliance

Decreased compliance: pulmonary congestion, interstitial pulmonary fibrosis, supine position, restrictive lung disease, pneumothorax, hydrothorax, asthma.
Increased compliance: emphysema, old age.

Surface Tension

Alveoli are lined with a thin layer of fluid with an interface between air and water.
Water molecules at the surface of the alveolar fluid have inward-pulling forces (surface tension) causing the alveoli to collapse.
Surfactant is a key factor preventing alveolar collapse.

Action of Surfactant

The presence of surfactant reduces surface tension.
Surfactant content in each alveolus is relatively constant. Lowering of surface tension when alveolus size decreases results in a similar pressure increase.
The action of surfactant is regulated by the law of Laplace (P = 2T/r).

Functions of Alveolar Surfactant

Stabilizes alveoli of varying radii.
Prevents collapse of alveoli during expiration.
Prevents pulmonary edema.
Increases lung compliance by reducing the centripetal force of surface tension in alveoli and increasing the lungs' stretchability.
Regulates lung inflammation and facilitates phagocytosis.

Surfactant

A lipid substance that reduces surface tension.
Primarily dipamitoylphosphatidylcholine (DPPC)
Mixture of other lipids and proteins
Prevents alveoli from collapsing during expiration and prevents pulmonary edema

Formation of Surfactant

Surfactant components are synthesized from precursors in the endoplasmic reticulum and transported via Golgi apparatus.
Transported through multi-vesicular bodies and packaged in lamellar bodies.
Release via secretion (exocytosis).
Components organize as a lattice (tubular myelin) within the alveoli.
This is believed to generate phospholipids necessary to create a monolayer at the air-liquid interface, lowering surface tension.

Metabolism of Surfactant

Phospholipids and proteins are subsequently absorbed by Type II cells, stored in lamellar bodies, then recycled and returned to the alveolar lumen.
Alveolar macrophages may take up some surfactant in the liquid layer as well.

Respiratory Distress Syndrome (IRDS)

A syndrome in newborns characterized by poor lung function due to the lack of sufficient surfactant.
Interventions to minimize risk:
- use of antenatal steroids
- appropriate resuscitation and use of CPAP
- Early administration of surfactant

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Description

This quiz covers essential aspects of the respiratory system, including the pleura, lung compliance, and the role of pulmonary surfactant. Test your understanding of the pleura's structure and function, lung compliance determinants, and clinical implications of surfactant in respiratory health.